1. Field of the Invention
This invention relates to a water-proof type photo-taking lens for an underwater camera, and particularly to a photo-taking lens for an underwater camera having a high imaging performance over a photographing distance range from infinity to a close distance at which close-up photographing is possible under water.
2. Related Background Art
When close-up photographing is to be effected under water, use has heretofore been made of an underwater camera having mounted thereon a close-up photographing apparatus integrally provided with a close-up lens and a field frame corresponding to the photographing range by the close-up lens, or an underwater photographing apparatus having a microlens capable of close-up photographing on a single-lens reflex camera contained in a housing for underwater photographing.
However, in an underwater camera having mounted thereon a close-up photographing apparatus comprising a close-up lens and a field frame, not only accurate confirmation of the photographing range has been difficult, but also the photographing magnification has been not very high and the aberration correction of the lens has been insufficient. On the other hand, in an underwater photographing apparatus having a single-lens reflex camera contained in a housing for underwater photographing, various aberrations occur in a water-proof window provided in the front face of the housing, and this has led to the disadvantage that the imaging performance of the camera is reduced.
Also, in recent years, attempts have been made to make an underwater camera into a single-lens reflex camera by making the most of the advantages of a single-lens reflex camera which is easy to focus and moreover is free of parallax even in close-up photographing. However, there is not yet known a photo-taking lens which is well corrected in aberrations for underwater use and suitable for use for close-up photographing.